Increase Modulation of GABA Receptors After Aerobic Exercise Intervention in Aging Adults

Research Objectives: Brain excitability is involved in learning, memory, and motor function and is maintained by increases (excitation) and decreases (inhibition) in firing rates of neurons, or E/I balance, which is largely mediated by inhibitory neurotransmitter gamma aminobutyric acid (GABA). GABA levels decrease during learning, increasing excitability, and return to baseline when the task is performed to automaticity. Aging, however, is associated with slower learning and increased GABA levels during the learning phase, indicating a loss of GABA inhibition. Exercise training may improve inhibition (GABA) during a learning task with coincident improvements in learning in older individuals. This study investigated the effects of a 12-week aerobic training intervention on GABA concentration and receptor function while learning a task and probed associations between GABA concentration and change in GABA receptor function using both magnetic resonance spectroscopy (MRS) and transcranial magnetic stimulation (TMS).

Design: In a cross-sectional design, participants were randomized to one of 2 groups, 12-week aerobic exercise intervention or 12-week low-intensity balance and stretching (control group).

Setting: Participants were recruited from the community.

Participants: Sixteen sedentary men (6) and women (10) having no history of neurological disease or upper-extremity impairments, and with normal cognitive-executive function were recruited. Average age was 69.88±4.63 years and BMI was 25.52±3.04 were randomized to a 12-week aerobic (3x/wk cycling) (n=8) or control group (balance and stretching exercises) (n=8).

Interventions: The aerobic intervention consisted of interval-based training on a stationary bike with intensity beginning at 50% of heart rate reserve (HRR) and increasing 5% weekly until reaching 75% HRR. The control group performed low-intensity body weight, stability balls, resistance bands, and stretching exercises. Duration of the training sessions for both groups increased from 20-45 minutes.

Main Outcome Measures: MRS was used to measure GABA concentrations and TMS was used to measure GABA receptor function during at rest, learning, and recall phases of a task.

Results: There was a significant difference in change of GABA concentration during Recall tasks between aerobic and control groups (0.41±0.69 and -0.29±0.66, p< 0.05, respectively). GABAa receptor response at baseline was positively associated with change in GABA concentration during recall (r=0.502, p< 0.05).

Conclusions: GABA concentration increased with aerobic training and decreased in the control group during the recall task, suggesting decreased inhibition during a motor learning task. Additionally, greater GABA concentration at rest may indicate greater change in GABA receptor response during a learning and memory task in older adults.

Author(s) Disclosures: N/A